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Unusual Behavior in GEO: SJ-17

This data repository accompanies Space Threat Assessment 2019, a featured report from the CSIS Aerospace Security Project.

This data repository visualizes the orbital position of Chinese satellite SJ-17 from January to September 2018, relative to other satellites currently in the GEO belt.

Unlike most objects in the geostationary belt, SJ-17 made a series of orbital maneuvers after it reached its destination orbital regime, varying its position relative to the Earth and neighboring satellites. In 2018, SJ-17 occupied a wide span of positions on orbit, from 37.7°E (corresponding to an orbital position overlooking eastern Africa) to 180°E (corresponding to an area overlooking the U.S. Marshall Islands).

In early 2018, defense news outlet Breaking Defense published a detailed list of SJ-17’s movements—provided by Analytical Graphics, Inc., an engineering software company—including a list of satellites that may have engaged directly with it through remote proximity operations (RPO).1 An adapted version of the table appears below.

To learn more about the potential consequences of such behavior on orbit, including a broader look at China’s counterspace weapon activities, read the China space threat assessment in Space Threat Assessment 2019.


This data visualization relies on two principal data sources: the catalog of all space objects, provided by the U.S. Strategic Command’s Combined Space Operations Center (CSpOC),3 and a database of geostationary satellites currently on orbit, provided by

The orbital position data for SJ-17 from January to September 2018—shown in orange in the interactive diagram—was derived from the two-line element (TLE) data for the satellite, available at The TLE for a space object is a measurement of the object’s approximate orbit (its inclination, right ascension of the ascending node, eccentricity, and argument of perigee) and its position on that orbit (its mean anomaly). This data was transformed into a time-dependent longitude position using PyEphem, a publicly-available Python package for high-precision astronomy computations.5 Although provides more than one TLE for SJ-17 per day during the time period depicted, this data repository shows just one longitudinal position per day, for clarity. Other data points were excluded at the author’s discretion.

The orbital position data for the other GEO satellites—shown in gray in the interactive diagram—use data from, as it appeared on March 24, 2019.

This interactive data repository is a product of the Andreas C. Dracopoulos iDeas Lab, the in-house digital, multimedia, and design agency at the Center for Strategic and International Studies.

Special thanks to Jacque Schrag for her work developing this tool.